The vertebrates in which blood flows directly from respiratory organs to body tissues without first returning to the heart are the ________.
A) amphibians
B) birds
C) fishes
D) mammals
E) reptiles

Question

Quizplus · Accepted Answer

This describes the circulatory system of fishes, where blood flows through the gills to pick up oxygen and then flows directly to the body tissues before returning to the heart. This type of circulation is known as single circulation. Amphibians, reptiles, and some non-avian dinosaurs also have single circulation, but their blood still passes through the heart before reaching the body tissues. Birds and mammals have double circulation, where blood flows through the heart twice before completing a full circuit of the body.

The Vertebrates in Which Blood Flows Directly from Respiratory Organs